Method for overlaying wood particle board



3,300,361 METHOD FOR OVERLAYIN G WOOD PARTICLE BOARD Gordon E. Brown, Seattle, Wash., assignor to Monsanto Company, a corporation of Delaware N Drawing. Filed Dec. 4, 1962, Ser. No. 242,079 4 Claims. (Cl. 156335) This invention is a continuation-impart of that claimed in copending application Ser. No. 790,342, filed February 2, 1959, now abandoned, and relates to a method for overlaying wood particle board. More particularly, this invention relates to a method of combining a highly wear and scuff resistant surface layer, having decorative value, and a wood particle board ibase into an article of manufacture having a desirable combination of properties.

In the selection of suitable materials for the decorative interior finishing of buildings some of the major problems are the lack of any material having the warmth and appeal of natural wood, a highly mar and scuff resistant surface, and a reasonable cost together with simple and rapid on-site installation procedures. Onsite finishing of natural wood is an obviously laborious task and the durability obtained leaves much to be desired. Manufactured sheet materials of the high density melamine type have the durability but are very costly and are difficult to install.

One object of this invention is to provide a material suitable for covering wall areas which has a smooth, hard surface impervious to the usual wear and tear while at the same time having the appeal of the varied grain patterns of natural wood.

Another object is to provide a method of surfacing composition board which will permit the formation of three dimensional contours and shapes during the pressing step of manufacture.

These and other objects are attained by uniting, under heat and pressure, a blank of wood particle board stock and a fibrous porous water softenable sheet impregnated and treated in a specific manner.

The following examples are given by way of illustration and are not intended as limitations on the scope of this invention. Where parts are mentioned they are parts by weight.

Example 1 Prepare an aqueous syrup by mixingtogether 100 parts of a dry melamine formaldehyde condensation product, 25 parts urea, 30 parts methanol, 50 parts water, 2 parts ammonium chloride, and 20 par-ts of saponified tall oil. Immerse inthis liquid wood veneer substantially one twenty-fourth of an inch in thickness, squeeze the veneer one or more times between rollers to force liquid into the interstices of the wood. Remove the veneer and air dry it to a moisture content of between 20% and 25%, based upon the original weight of the dry sheet. Position this partially dried veneer :between a metal caul, preferably of stainless steel, and a blank of commercial wood particle board having a specific gravity of approximately 0.67. Press the assembly in a heated platen press at a temperature of approximately 300 degrees Fahrenheit and a pressure of approximately 200 pounds per square inch for a period of substantially 8 minutes. After the pressure has been on for approximately 2 minutes it can be reduced to as low as 50 pounds per square inch for the remainder of the 8 minute period.

The article so prepared has a smooth, hard surface that can not be scratched with the thumb nail nor rupt-ured by the edge of a coin drawn firmly over it. The

United States Patent a 3,300,361 Pa'te'n'ted Jan. 24, 1967 wood veneer has attained a state of polish resembling a hand-rubbed finish. Surface voids which would ordinarily require filling have been closed by densification of the wood and/or filled with clear resin.

Example II Prepare an aqueous syrup by mixing together, parts of a condensation product of phenol and formaldehyde possessing at least limited compatibility with water, such as Monsanto PF594, 25 parts of methanol and 5 parts of an alkali metal soap. Immerse in this solution a porous, absorptive pulp sheet consisting of intertwined cellulose fibers, until the sheet is substantialy impregnated with the liquid. Dry the sheet in an oven at substantially degrees Fahrenheit until the surface thereof is no longer wet but the water content of the sheet is above about 20% based on the original weight of the dry sheet. Position this treated sheet between a metal caul or die and a blank of commercial wood particle board having a specific gravity of approximately 0.40. Press the assembly in a heated platen press at a temperature of substantially 380 degrees Fahrenheit and a pressure of substantially 300 pounds per square inch for a period of substantially 12 minutes. During the pressing step the density of the assembly will increase, due to the compression, to yield the more desirable specific gravity of about 0.75. The article so prepared has a hard wear and chemical resistant surface consisting of consolidated fiber and thermoset phenol formaldehyde resin.

My method has a number of distinctions and advantages over ordinary prior art methods of overlaying backing material. Overlayment of particle board by gluing decorative wood veneer thereto yields a product which must be substantially flat and which needs sanding, filling and finishing before ultimate end use. The finish is more or less vulnerable to damage in average use. High pressure melamine-formaldehyde and phenolformaldehyde decorative laminates are manufactured under elaborate methods to eliminate the volatiles which would cause severe blistering in the pressing step. Prior art methods using impregnated overlays require, in various embodiments, substantial cure of the overlay sheet prior to lamination, use of an auxiliary binder, and sheets of relatively low water content at time of overlay; each of which presents difficulties and disadvantages avoided in the present method. Resins are accordingly applied to a plurality of paper sheets, each of which must be vigorously dried and freed of volatiles prior to pressing. In the absence of moisture, expensive nonvolatile plasticizers are necessary to insure adequate resin flow and consolidation. Moreover, the finished laminate must be affixed to a backing of material of some thickness, such as plywood or particle board, in a separate operation. In the case of plywood backing, special low pressure glues and gluing procedures are essential to prevent the telegraphin-g of the grain configuration to the surface.

These difficulties are overcome by the procedures disclosed herein.

The use of veneer stock substantially thinner than that conventionally used in overgluing is possible because no sanding is subsequently performed, and is preferable to minimize material cost and maximize deformability.

Water in the veneer and in the resin impregnant is an intrinsic and essential factor in this proces. It promotes resin flow and consolidation, it enhances the ease of parting from cauls, it softens the wood structure of the veneer to allow densification under heat and pressure and deformation to the contour of the caul, it travels from the veneer during pressing to carry resin to the veneer-particle board interface to provide an adhesive bond, it provides a solvent medium for the wood plasticizer, urea, and it provides a low cost, convenient vehicle for the application of the resin. It is an essential limita tion of the method of this invention that the resin impregnated porous water softenable sheet have a moisture content of at least based upon the original weight of the dry sheet, at the time of application to the particle board substrate in order that the foregoing functions of moisture in the system be efiiciently effected.

More particularly, it has been found that the structures resulting from the use of overlay sheets having the above moisture content of at least 20% possess surfaces exhibiting significantly greater resistance to abrasion than do corresponding structures manufactured using sheets of lesser moisture content. In this regard, it has been found that optimum results are attained at moisture levels of from about 20 to The use of particle board backing provides a place for the water to go that is introduced with the impregnated surface veneer, thus obviating the need to eliminate volatiles before pressing. Particle board of the preferred specific gravity of 0.60 to 1.0 has the advantage of not densifying as much as solid soft-wood or plywood under heat and pressure. It has the further advantage of being more permeable in a direction laterally across its thickness than plywood or solid wood. The absence of any well defined growth rings enables particle board to withstand pressure uniformly without deformation or telegraphing related to grain structure. Particle board is also free of knots, pitch pockets and other defects which would be highly detrimental.

The resins used in this process are limited to water dispersible, thermosetting, synthetic products used in liquid aqueous systems and retaining a definite quantity of entrained water until pressed. The inclusion of stains, flatting agents, abrasives and fire retardants, as desired, are within the scope of this invention. Similarly, the use of sheet materials other than wood veneer is contemplated, provided that a porous structure is evident within the sheet and provided that softening, densifying and consolidating said sheet in a continuous matrix of resin is a basic objective.

The wood particle board used in my process is preferably a board formed by the consolidation, under heat and pressure, of wood fiber and/or particles together with thermosetting resin or protein binder, to a solid integral article having a specific gravity of 0.40 to 1.0. Materials may be incorporated during manufacture of the particle board to provide fire resistance or termite or mold resistance without changing the scope of this invention.

Various components of the impregnating liquids are materials commonly used to impart characteristics which are well-known to those skilled in the art. Methanol is used to lower viscosity and surface tension and thus, improve impregnation, or to hasten the drying step. Ammonium chloride is a well-known acidic catalyst used to promote the thermosetting of urea or melamine resins. Urea has long been recognized as a softener or plasticizer for Wood. Various soaps, oils and waxes are commonly used as parting agents to promote the clean and easy separation of a die from a heat formed article.

The manufacturing conditions with respect to water content, temperature, pressure, press time and particle board density are preferably restricted in range and scope; however, it will be apparent to those skilled in the art that the said conditions are, in fact, interrelated in such a way that any one of them may be increased or decreased in magnitude, with satisfactory results, by simultaneously altering one or more of the other conditions in a compensating direction. For example, increase of temperature, pressure, water content or press time will increase densification, while higher temperatures and lower moisture contents permit shorter press times, etc.

Obviously, many changes may be made in the products, processes and methods heretofore set forth without departing from the spirit and scope of this invention.

What is claimed is:

1. The process of overlaying particle board with a durable surface, comprising applying a liquid aqueous solution containing a thermosetting resin selected from the group consisting of melamine-formaldehyde resins and phenol-formaldehyde resins onto and into a fibrous porous water softenable sheet; applying said sheet to a wood particle board backing while the moisture content of the sheet is within the range of from 20 to 25% based upon the dry weight of the sheet; and pressing the assembly at 200 to 380 degrees Fahrenheit for two to twelve minutes at a pressure of 50 to 300 pounds per square inch.

2. The process as claimed in claim 1 wherein the water softenable sheet is wood veneer.

3. The process as claimed in claim 1 wherein the thermosetting resin is melamine-formaldehyde resin.

4. The process as claimed in claim 1 wherein the thermosetting resin is phenol-formaldehyde resin.

References Qited by the Examiner UNITED STATES PATENTS 2,425,660 8/ 1947 Ware et al. 156549 X 2,565,251 8/1951 Malmstrom 16156 2,593,708 4/1952 Ware et a1. 156324 X 2,801,198 7/1957 Morris et al.

2,831,794 4/1958 Elmendorf 156312 X 2,931,750 4/1960 Goms 156-312 2,977,272 3/1961 Pounds 161231 X 3,011,938 12/1961 Chapman 15662.2

EARL M. BERGERT, Primary Examiner.

C. B. COSBY, Assistant Examiner. 

1. THE PROCESS OF OVERLAYING PARTICLE BOARD WITH A DURABLE SURFACE, COMPRISING APPLYING A LIQUID AQUEOUS SOLUTION CONTAINING A THERMOSETTING RESIN SELECTED FROM THE GROUP CONSISTING OF MELAMINE-FORMALDEHYDE RESINS AND PHENOL-FORMALDEHYDE RESINS ONTO AND INTO A FIBROUS POROUS WATER SOFTENABLE SHEET; APPLYING SAID SHEET TO A WOOD PARTICLE BOARD BACKING WHILE THE MOISTURE CONTENT OF THE SHEET IS WITHIN THE RANGE OF FROM20 TO 25% BASED UPON THE DRY WEIGHT OF THE SHEET; AND PRESSING THE ASSEMBLY AT 200 TO 380 DEGREES FAHRENHAIT FOR TWO OR TWELVE MINUTES AT A PRESSURE OF 50 TO 300 POUNDS PER SQUARE INCH. 